The R300/R400 GPUs don't yet have HyperZ support enabled by default until sufficient testing has been completed, but the HyperZ support can be toggled via the RADEON_HYPERZ environment variable. The newer Radeon GPUs with the R600g Gallium3D driver also don't yet have usable HyperZ support enabled by default. HyperZ is the ATI/AMD technology that's been around going back to the R100 GPU days for boosting the GPU performance and efficiency. HyperZ consists of Z compression for minimizing the Z-Buffer bandwidth, fast Z clear, and a hierarchical Z-Buffer.

In the Git commit enabling this feature, Marek describes the support as:

- Only one process can use it at a time. This is a hardware limitation.
- The first process to clear a zbuffer gets the exclusive access to use Hyper-Z.
- Compositors don't use any zbuffer, so they won't steal it, but some web browsers do, so make sure there's no web browser running if you want your game to use Hyper-Z.
- There's no need to restart an app which couldn't get the access to Hyper-Z. Just quit the app which took it, the driver can turn it on for the other app in the middle of rendering.
- If an app gets the access to Hyper-Z, it prints "radeon: Acquired Hyper-Z" to stdout.

I did some HyperZ benchmarks months ago, but new R300g performance tests will now be coming up.

Michael Larabel is the principal author of Phoronix.com and founded the web-site in 2004 with a focus on enriching the Linux hardware experience and being the largest web-site devoted to Linux hardware reviews, particularly for products relevant to Linux gamers and enthusiasts but also commonly reviewing servers/workstations and embedded Linux devices. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics hardware drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated testing software. He can be followed via Twitter and Google+ or contacted via MichaelLarabel.com.